1. Field of the Invention
This invention relates to the field of reinforced glass structures in general, and in particular, to laminated safety glass reinforced with ionomer resin films and/or polycarbonates. Laminates of glass, ionomer resin and metal are also contemplated in the invention.
2. Description of Prior Art
Safety glass can be reinforced by lamination with an inner layer of polycarbonate. The resulting lamination, however, is impractical for two principal reasons. One reason is insufficient bond strength when the polycarbonate is bonded directly to the glass. A second, and even more important reason stems from polycarbonate and glass having different co-efficients of thermal expansion. Safety glass laminates may be bonding polycarbonate directly to glass will crack and craze on cooling from the temperature necessary to bond the two together, due to the different thermal expansion co-efficients of the components.
Initial attempts to solve these problems involved interposing additional interlayers of polyvinyl butyral between the polycarbonate and the glass. Adhesion between the polycarbonate and the glass proved insufficient unless a plasticizer was also used. However, when a plasticizer was used, the plasticizer often caused the polycarbonate to develop stress cracks, and accordingly, to have low light transmission properties.
The initial problems appear to have been solved in the laminated safety glass described in U.S. Pat. No. 3,888,032, which has achieved wide commercial success. The laminate comprises polycarbonate reinforced glass wherein the polycarbonate and glass are bonded to one another by an interlayer of polyurethane. Polyurethane provides sufficient adhesion to glass and to the polycarbonate, and no stress cracking or cloudiness develops in the product.
Despite the commercial success of the polyurethane laminated product, there has been a continuing effort to develop less expensive products, particularly as polyurethane is an expensive component. This invention provides new glass laminates, with and without layers of polycarbonates, and other reinforcing transparent plastics, which are considerably less expensive than the polyurethane laminates, yet which at the same time are every bit as satisfactory, if not more so, with regard to adhesion, strength and clarity. Laminates according to this invention comprise at least one layer of glass laminated with an iomoner resin film.
In the specification and claims the terms "ionomer" or "ionomer resin" mean an extrudable resin comprising ionically crosslinked ethylene-methacrylic acid copolymers; and more particularly, sodium or zinc crosslinked ethylene-methacrylic acid copolymers. Properties which distinguish ionomer resins from other polyolefin heat-seal polymers are high clarity, melt strength, solid-state toughness and resistance to oil/fat permeation. Ionomer resins are generally available as either a sodium or a zinc ionomer, and are available in a wide variety of grades. Amine ionomers are also produced. Although all grades of ionomer resins generally exhibit the properties noted above when compared to other heat-sealed polymers, sodium ionomers are known for exceptional toughness and resistance to fats and oils, while zinc ionomers exhibit outstanding adhesion to unprimed foil and process excellent chemical resistance. Sodium ionomers have proved to provide the best clarity, the zinc ionomers proving hazy at times.
Various grades of ionomer resins are available for extrusion coating and film extrusion. It is also known that ionomer resins can be co-extruded with other plastic resins and exhibit adhesion to other polyolefins, nylon resins and coextrudable adhesive resins often used as bonding layers in multi-ply coextruded structures. A very wide variety of ionomer resins are manufactured by E. I. DuPont de Nemours and Company under the registered trademark "SURLYN".
Ionomer resins have been suggested for use primarily in the area of packaging, for foods, liquids and pharmaceuticals, as well as certain industrial applications including lightweight sails, bonded cable sheath, roof underlayment and flame retardant products. In most applications, ionomer resins ae offered as superior substitute for polyethylene. In none of the literatur or prior art is there any suggestion that ionomer resins should or could be used for reinforcing glass layers or for bonding layers of glass to polycarbonate or other plastic layers, in order to form a laminated safety glass. Moreover, there is no suggesion in the literature or prior art indicating the ionomer resins could or should be substituted generally for polyurethanes.
Layers of ionomer resins can be formed by casting or extrusion, the latter being preferred. One formed there are no significant differences between cast and extruded layers. When the ionomer resin layers are sufficiently thick, polycarbonate layers can be eliminated altogether.
Ionomer resins have several advantages over polyurethane. Polyurethane is difficult to manufacture and hard to fabricate. It is frequently not clear enough for use in windshields and the like. By contrast, ionomer resin films can be easily extruded to desired thicknesses, and at about one-half the material cost of polyurethane. Ionomer resins have demonstrated better adhesion characteristics to polycarbonates, as well as better resistance to lower temperatures. In preferred embodiments, the surface to which the ionomer resin is adhered may be primed to get good adhesion, as is the case with polyurethane. Silane coupling agents are suitable primers. With regard to optical properties, ionomer resins demonstrate better clarity than polyurethane. Moreover, the ionomer resins are more hydrolytically stable to water, acids and bases, are more resistant to degradation from ultraviolet light, and overall, are less likely to weaken with time. This greatly enhances the useful life of laminates made in accord with the present invention.